This is a revised competing renewal application for support of Years 3 - 5 of an ADAMHA RSDA (Level II). The material contained in the revision that specifically addresses critical comments in the Summary Statement is outlined in the Introduction. By way of general background, the PI moved from the University of Massachusetts (Amherst) to Pennsylvania State University (University Park) in the summer of 1994. The work to be done at the new institution is consistent with what was originally planned for the corresponding portion of the RSDA period. Support for the final three years of the RSDA will allow the PI to continue his intensive study of the cognitive control of human movement, which he pursued earlier in a 5-year nonrenewable RCDA from NINDS and which has continued apace during the first two years of the RSDA. The PI is one of the only cognitive psychologists in the world studying the planning and control of physical behavior, so his opportunity to carry out research at the level made possible by an RSDA has special importance for the advancement of this small but important field. The focus of the PI's project is a new theory of movement planning. The theory is designed to explain how limb segments are recruited for reaching and other tasks. The assumed computations allow limb segments to compensate automatically for reduced mobility of other segments, but they also explain a wide range of other facts concerning practice movement speed, required accuracy. sequencing of behaviors, anticipation, and other phenomena. The theory also predicts a number of new effects which have been tested in the PI's laboratory and which will continue to be tested using new behavioral experiments, including a new type of experiment in which subjects carry out movements in a virtual reality setting. These experiments will make it possible to analyze aspects of behavior that have received virtually no prior attention, notably the timing of joint movements and reaching around obstacles. Extensions of the theory will also be pursued in the domains of walking, speaking, and sign language. Although the planned research ostensibly focuses on motor control. it draws upon and will contribute to other branches of cognitive and neural science, including those branches in which the evaluation of mental health relies on the analysis of motor behavior. Besides enabling the PI to work in a concerted way on his research, the RSDA will allow him to audit courses and interact extensively with his many new colleagues at Penn State, especially the large group of outstanding biomechanists at University Park. The RSDA will also allow the PI to visit other institutions in order to interact with distinguished researchers, continue his ongoing research collaborations, and engage in other research-related activities.